Instron 2603-080, Справочное руководство

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Description
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Description
Principle of Operation
Operation of the Long Travel Elastomeric Extensometer is based on a pair of separately
counterbalanced clamp assemblies (see
Figure 1-1 ) which attach to the specimen.
The clamp assemblies are mounted on carriages. Their vertical position on the carriages can
be adjusted, with the carriages touching, to set the gauge length. The horizontal position of
the clamp assemblies can also be adjusted to allow for different specimen thicknesses. The
clamping force on the specimen can be varied and the clamps are designed to release at
specimen break.
Cables run from each carriage over precision machined pulleys in the head of the unit and
into support tubes. Inside the support tubes, weights counterbalance each clamp assembly.
One pulley carries the body of a rotary potentiometer, the other pulley is fixed to the
potentiometer shaft.
The carriages are guided by linear bearings on a ground and polished rod. This feature,
along with careful counterbalancing of each assembly, prevents any of the extensometer’s
weight being applied to the specimen.
The precision, single-turn potentiometer tracks the differential movement between the two
clamp assemblies. The excitation voltage, generated by the testing machine, is applied to the
potentiometer. The potentiometer wiper voltage is buffered and applied to a resistor bridge.
Thus the output voltage from the extensometer is proportional to the specimen extension.
Mechanical stops fitted to the pulleys prevent overtravel of the potentiometer.
Basic Features
•
The upper and lower specimen clamp assemblies are accurately counter-balanced so that
the extensometer applies a load of only 0.15 N (15 g) when attached to the specimen and
should therefore have negligible effect on test results.
•
Variable gauge length settings can be obtained. The calibration bar supplied with the
extensometer provides a range of settings. See Appendix
A for specification details.
•
The clamp assemblies can be moved vertically on carriages and are locked at the
required gauge length by knurled thumb nuts.
•
The horizontal position of the clamp assemblies can be adjusted, using knurled
thumbscrews, to allow for different specimen thicknesses.
•
The specimen gripping force is adjustable.